School of Chemistry, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
Chemistry. 2013 May 17;19(21):6613-29. doi: 10.1002/chem.201204453. Epub 2013 Mar 27.
New complexes with six ferrocenyl (Fc) groups connected to Zn(II) or Cd(II) tris(2,2'-bipyridyl) cores are described. A thorough characterisation of their BPh4(-) salts includes two single-crystal X-ray structures, highly unusual for such species with multiple, extended substituents. Intense, visible d(Fe(II))→π* metal-to-ligand charge-transfer (MLCT) bands accompany the π→π* intraligand charge-transfer absorptions in the near UV region. Each complex shows a single, fully reversible Fe(III/II) wave when probed electrochemically. Molecular quadratic nonlinear optical (NLO) responses are determined by using hyper-Rayleigh scattering and Stark spectroscopy. The latter gives static first hyperpolarisabilities β0 reaching as high as approximately 10(-27) esu and generally increasing with π-conjugation extension. Z-scan cubic NLO measurements reveal high two-photon absorption cross-sections σ2 of up to 5400 GM in one case. DFT calculations reproduce the π-conjugation dependence of β0, and TD-DFT predicts three transitions close in energy contributing to the MLCT bands. The lowest energy transition has octupolar character, whereas the other two are degenerate and dipolar in nature.
新的配合物具有六个连接到 Zn(II) 或 Cd(II) 三(2,2'-联吡啶)核的二茂铁基(Fc)基团。对其 BPh4(-)盐进行了彻底的表征，包括两个单晶 X 射线结构，对于具有多个扩展取代基的此类物种来说非常不寻常。在近紫外区域，强烈的可见 d(Fe(II))→π金属-配体电荷转移 (MLCT) 带伴随着π→π 内配体电荷转移吸收。每个配合物在电化学探测时都显示出单个完全可逆的 Fe(III/II)波。通过使用超瑞利散射和斯塔克光谱法确定了分子二次非线性光学 (NLO) 响应。后者给出了静态第一超极化率 β0，高达约 10(-27) esu，通常随着 π 共轭延伸而增加。Z 扫描立方 NLO 测量在一种情况下揭示了高达 5400 GM 的高双光子吸收截面 σ2。DFT 计算再现了 β0 的 π 共轭依赖性，并且 TD-DFT 预测了三个能量接近的跃迁对 MLCT 带有贡献。最低能量跃迁具有八极子特性，而另外两个跃迁在性质上是简并的和偶极子的。
